Molded-case electric circuit breaker



April 12, 1966 J 5, HALL 3,246,098

MOLDED-CASE ELECTRIC CIRCUIT BREAKER Filed July 15, 1964 3 Sheets-Sheetl 75 INVENTOR.

JOHN S. HALL Y Q/M a. mama-v A ril 12, 1966 J. s. HALL 3,246,098

MOLDED-CASE ELECTRIC CIRCUIT BREAKER Filed July 15, 1964 3 Sheets-Sheet2 INVENTOR.

1 JOHN S. HALL April 12, 1966 J. s. HALL MOLDEDCASE ELECTRIC CIRCUITBREAKER 3 Sheets-Sheet 5 Filed July 15, 1964 km Wm INVENTOR. JOHN s.HALL United States Patent 3,246,4298 MQLDED-CASE ELECTRIC ClRCUlTBREAKER John S. Hall, Aldbcurne, England, assignor, by mesneassignments, to Square E) Company, Park Ridge, 151., a corporation ofMichigan Filed Early 15, 1964, Ser. No. 382,732 Claims priority,application Great Britain, Mar. 13, 1964, 10,6ltl/54 9 Claims. (Cl.Mil-8d) This invention relates generally to electric circuit breakers,and more particularly to a thermally and magnetically responsive circuitbreaker of the molded case variety suitable for controlling theautomatic opening of branch circuits rated as low as five amperes at 240volts.

Automatic electric circuit breakers of the type disclosed in BritishPatent No. 893,282, published April 4, 1962, are often installed toprotect relatively low voltage and low power circuits, as found, forexample, in residential and small commercial buildings, against overloadand fault conditions. Basically, such a circuit breaker comprises a pairof separable contacts, a springoperated mechanism for eifectingseparation of the con- 0 tacts, and a trip device that automaticallyreleases the operating mechanism upon the occurrence of predeterminedconditions in the electric circuit in which the circuit breaker isconnected.

One form of trip device often utilized in circuit breakers of thegeneral type disclosed in the aforementioned patent comprises athermally responsive element in the form of an elongated bimetallicstrip arranged to carry the current of the circuit to be protected andwhich, upon continuation of a moderate overload, heats sufficiently toflex and thereby release the spring-actuated contact-operatingmechanism. The trip device also includes a magnetic assembly thatbecomes operative upon the occurrence of a severe overload or a faultcondition in the circuit to release the operating mechanism more quicklythan can the thermally responsive element. Such former circuit breakershave been designed to operate satisfactorily in branch circuits rated atfifteen amperes, 120 volts, but these former circuit breakers will notoperate satisfactorily to protect branch circuits rated at five amperes,240 volts.

Accordingly, the principal object of the present invention is to providea trip device of increased sensitivity that is rendered operative uponflow of a relatively low overload or fault current to open the contactsof a circuit breaker.

Circuit breakers are mounted in panelboards which have becomestandardized in design, and thus the exterior dimensions orconfiguration of circuit breakers must be such that they can be acceptedin the panelboard. Therefore, it is important that any improvement orchange in the trip device of a circuit breaker be accomplished withoutnecessitating a change in a critical external dimension or configurationof the circuit breaker.

Because of cost and installation space requirements, the electricalspacing between conductive components of a circuit breaker is already atthe acceptable minimum and cannot be materially reduced without reducingthe rating of the circuit breaker. Therefore, in order to maintain thecritical external dimensions, a trip device operable at lower currentspreferably has the same general configuration as the trip device it isto replace and the size is restricted. Further, operation at highervoltages increases the difficulty of extinguishing arcs that occur uponcontact separation. In order to maintain the critical exteriordimensions of higher voltage circuit breakers, a rearrangement ofcircuitry through the circuit breaker Patented Apr. 12, 1966 isnecessary to provide space for a larger arcing chamber and de-ionizingplates.

Another object of the present invention is to provide a trip device ofincreased sensitivity and a larger arcing chamber for a circuit breakerof lower current and higher voltage rating without requiring a change ina critical dimension of the circuit breaker, thereby enabling thecircuit breaker to be used in the same size electrical panelboard ascircuit breakers of lower voltage and higher current rating.

One method of increasing the sensitivity of the fault current responseof a trip device comprising a magnetic core and an associated armature,and wherein a magnetic flux is induced in the magnetic core by anelectrical conductor, is to increase the effective ampere turns withrespect to the core. Since the amount of current is determined by thecircuit in which the circuit breaker is used, the effective ampere turnscan be increased only by increasing the number of turns of theelectrical conductor about the core. Because the exterior dimensions ofthe trip device cannot be materially increased, the increased number ofturns must be accommodated substantially within the confines of theoriginal trip device.

Another object of the present invention is to provide a trip device inwhich a thermally responsive conductor and a non-thermally responsiveconductor are electrically connected in series and are supported incooperative relation with a magnetic core and with each other to providea plurality of turns about the core without increasing a criticaldimension of the circuit breaker, thereby enabling the circuit breakerto be used in the same size electrical panelboard as circuit breakers oflower voltage and higher current rating.

Another object is to provide an improved trip device comprising amagnetic yoke through which a thermally responsive element in the formof a bimetallic strip extends and wherein the operative fiux in the yokeis developed in part by current flowing through the thermally responsiveelement and in part by current flowing through a conductor wound aboutone leg of the yoke and electrically in series with the thermallyresponsive element.

A further object is to provide an improved trip device comprising athermally responsive bimetal that responds to heat developed byrelatively small currents.

Yet another object is to provide an improved magnetic core and armaturesupport which is deformable in accordance with the size of air gaprequired to provide a circuit breaker having a desired magnetic trippoint.

Other objects and advantages of this invention will become apparent fromthe following description wherein reference is made to the drawings, inwhich:

FIG. 1 is a view of a circuit breaker constructed in accordance withthis invention, the cover having been removed, certain parts being shownin section, and the mechanism being shown in on position;

FIG. 2 is a sectional view taken generally along the line 2-2 of FIG. 1but including the cover;

FIG. 3 is a fragmentary sectional view taken generally along the line3-3 of FIG. 4 but including the cover;

FIG. 4 is a fragmentary view similar to FIG. 1 but showing the mechanismof the circuit breaker in tripped' position;

FIG. 5 is a view similar to FIG. 4 but showing the mechanism of thecircuit breaker in off position;

FIG. 6 is a fragmentary view of the combination magnetic core andarmature support and certain associated parts of the circuit breaker ofFIG. 1 as viewed from the left in FIG. 1;

FIG. 7 is a fragmentary view similar to the righthand portion of FIG. 1but showing a second embodiment of the invention;

FIG. 8 is a sectional view taken genenally along the line 88 of FIG. 7but including the cover;

FIG. 9 is a view of the line terminal and certain associated parts ofthe circuit breaker of FIG. 7 as viewed from the left in FIG. 7;

FIG. 10 is a view similar to FIG. 7 but with certain portions brokenaway;

PEG. 11 is a view similar to FIG. 10 but illustrating an adjusted airgap between the armature and core of the circuit breaker; and

FIG. 12 is a perspective view of the combination magnetic core andarmature support of the circuit breaker.

FIGS. l6 show an embodiment of the invention for low current ratings.The molded case of the circuit breaker of FIGS. 1-6 includes a base 26*and a cover 21 molded of insulating material and secured together by aplurality of rivets 22. The base and cover are provided with moldedrecesses and barriers for supporting the other parts of the circuitbreaker, as will be understood.

A load terminal including a shiftable connector body 24 and a clampingscrew 25' is provided adjacent one end of the case. The clamping screwbears against one side of an end portion of a terminal strap 2 3 to movethi connector body and clamp a wire (not shown) between the connectorbody and the other side of the terminal strap.

A stationary contact 23 is secured to the other end portion of theterminal strap 26 for cooperation with a movable contact 3%) secured tothe bight portion of a generally U-shaped contact arm 32 pivotallysupported in a pair of inwardly extending spaced leg portions 33 of anoperating handle 34 pivotally supported in the base 2%? and cover 21. Ahole 35 is provided in the handle 34 for the reception of a handle tiebar (not shown) when it is desired to provide a multiple circuit breakersimilar to that shown in British Patent No. 827,740, published February10, 1960.

A slid able arc shield member 36 formed of insulating material is hookedto the contact arm 32. An overcenter tension spring 38 is hooked at oneend to the bight portion of the contact arm 32 and at the other end to agenerally U-shaped releasably latehable cradle member or trip lever 4t?pivotally mounted adjacent one end on a projection 41 of the base 20between the load terminal 24 and the contact arm 32 and releasablylatehable at the other end in a slot 43 of an armature member 44provided with a reversely bent tail portion 45. The trip lever 49 extendthrough the handle 34 between the spaced leg portions 33 and carries areset pin 46 cooperable with the leg portions 33 in the resetting orrelatching of the trip lever after it has tripped. A hole 48 is providedin the trip lever for the reception of a pin (not shown) cooperable witha common-trip crossbar (not shown) mountable in the base 2t and cover 21when knockouts such as the knockout 5d shown in the base 2% are removedto provide a mul'tipole circuit breaker similar to that shown in theaforesaid Patent No. 827,740.

The armature dd is provided with a thin generally Z- shaped latch plate52 extending through the slot 43 and having opposite end portionssecured to opposite sides of the armature on opposite sides of the slot.The latch plate 52 is shown as being thicker than it is in actualpractice due to limitations of drawing.

In accordance with the invention and as best shown in FIG. 12, acombination magnetic core and armature support is provided whichincludes a relatively large generally U-shaped magnetic core portion 54,a smaller generally U-shaped armature support portion 55, and aconnecting portion 56 extending along the inner surface of the base 2%and connecting one leg portion of the m agetic core portion 54 with acorresponding leg portion of the armature support portion 55. Acylindrical projection 58 on the base 20 extends through an opening inthe connecting portion 56 and the adjoining leg of the armature supportportion 55, and a tongue 59 extend ing oppositely of the connectingportion 56 from the adjoining leg of the magnetic core portion 54- isanchored or received in a recess in a boss 60 on the base 2i? t securethe magnetic core and armature support in position between the base 29and cover 21. The armature 44 is pivotally supported on the armaturesupport portion 55 and is biased clockwise as viewed in FIGS. 1, 4, and5 by a helical compression spring 62 seated in a wall portion of thebase 29.

A line terminal 64 is provided adjacent the other end of the case fromthe load terminal 24. In the embodiment shown, the line terminal 64- isgenerally Ushaped as shown in FIG. 6 to provide a pair of plug-in typeterminal jaws. A solid wire conductor 66 is secured at one end to theline terminal 64 and is wound several times around the leg portion ofthe magnetic core portion 54 opposite the connecting portion 56 andaround an insulating sleeve s7 thereon and is secured at the other endto one end of a mounting bracket 68 held in position against a pair ofrounded raised bearing portions 71 and 73 on an end wall portion of thebase 26 by a screw 69. A bimetallic member is secured at one end to theother end of the bracket es and extends through the magnetic coreportion 5 between the legs thereof.

The bracket 68 is resilently deformable by rotation of the screw 6? tovary the position of the free end of the bimetallic member 7% withrespect to the tail portion 45 of the armature 44- and thus calibratethe thermal tripping point of the circuit breaker. A flexible braidedwire conductor or cable 72 is secured at one end to the other or freeend of the bimetallic member 76 and is secured at the other end to thecontact arm 32.

An are chute assembly including a plurality of deionizing plates 7 heldin spaced relationship to each other in a form-ed insulating fiberboardenclosure '75 is provided for the separable contacts .13 and 30. Thebase 20 is provided with a pair of vent passages 76 and 77 extendingfrom opposite sides of the arc chute assembly, the passage '77 ventingbetween the jaws of the line terminal 64. A mechanical mounting clip 78is provided adjacent the other end of the case from the line terminal64.

Movement of the handle 34 from the position shown in FIG. 1 to theposition shown in FIG. 5 shifts the pivot point of the contact arm 32across the axis of the spring 33 and causes the spring to pivot thecontact arm to the off position, and conversely, movement of the handleback to the position of FIG. 1 causes the spring to pivot the contactarm back to the on position.

Pivoting the armature counterclockwise as viewed in E16. 1 unlatches thetrip lever ii} and causes the spring 38 to pivot the contact arm 32,handle 3d, and trip lever id to their tripped positions shown in 1 1G.Movement of the handle toward the cit position of PEG. 5 causes the legportions 33 to pivot the reset pin 45 counterclockwise in FIG. 4 aboutthe projection 41 to reset or relatch the trip lever.

The unlatching of the trip lever as from the latch plate 52 in the slot43 of t 1% armature 34 may be caused either thermally by engagement ofthe free end of the bimetallic member '70 with the tail of the armatureupon sustained moderate overload current or magnetically by sufficientenergization of the magnetic core portion 54 upon a heavy overload suchas that caused by a short circuit current.

It wiil be noted that the line terminal 64 and load terminal 24 arereversed with respect to the operating mechanism from their positions asshown in the circuit breaker of the aforesaid Patent No. 893,282, that alarger arc chute has been provided.

The thermal and magnetic tripping unit herein discosed lends itself veryreadily to production of circuit breakers of various current ratings.Thus, for the lowest rating, a relatively large number of turns may beprovided in the winding of the conductor 66 about the magnetic coreportion 54 to produce sufiicient magnetic flux to trip the circuitbreaker upon occurrence of relatively low short circuit currents, andthe conductor 66 may be made of nickel-chromium or other high resistancewire to produce additional heat for activating the bimetallic member 70upon relatively low sustained overload currents. For progressivelyhigher ratings, fewer turns may be provided in the conductor 66, and thematerial thereof may be changed to copper to reduce the heat input tothe bimetallic member 70. For still higher ratings, the constructionshown in the modification of FIGS. 711 may be used.

In FIGS. 7-11, the conduct-or 66 has been replaced by a formedconductive strap member 80 secured at one end to the line terminal 64and extending outside of the magnetic core portion 54 to the mountingbracket 68 to which its other end is secured. The strap member 80,bracket 68, and bimetallic member 70 thus provide merely one turn forthe magnetic circuit defined by the magnetic core portion 54 and thearmature 44. The number of turns cannot be further reduced withouteliminating the magnetic flux, but circuit breakers with still highercurrent ratings may be produced by increasing the air gap as best shownin FIGS. 10 and 11. Thus, the connection between the tongue 59 and itsassociated leg of the magnetic core portion 54 is weakened by theforming of a recess in one side of the tongue, leaving a relativelynarrow connecting portion 82 joining the rest of the tongue to themagnetic core portion. The connecting portion 82 may be laterally bentin one direction be fore assembly of a circuit breaker to increase theair gap in the assembly and thus produce a circuit breaker with a highermagnetic trip point, or the connecting portion may be bent in anopposite direction to decrease the air gap. In FIG. 10, the armature 44is shown in the relative position it assumes when latched, and an angleA is shown between the armature and the magnetic core portion 54. InFIG. 11 the angle A has been increased by bending of the connectingportion 82 before assembly of the circuit breaker, thus increasing theair gap and producing a circuit breaker having a higher magnetic trippoint.

The distance between the line terminal 64 and the mounting clip 78 hasbeen maintained the same as in the circuit breaker of the aforesaidPatent No. 893,282, and the distance between the handle 34 and the lineterminal 64 and mounting clip 78 has also been maintained the same as inthe aforesaid patent, although the line terminal and mounting clip havebeen reversed from their positions in the aforesaid patent relative tothe handle. Thus the circuit breaker of this invention and that of theaforesaid patent can be used with the same size panelboard, yet thecircuit breaker of this invention has been provided with a larger arcchute so as to be able to handle higher voltages and with a trippingdevice capable of operating both thermally and magnetically at lowercurrents than the corresponding currents of the prior device of theaforesaid patent.

Various modifications may be made in the structure shown and describedwithout departing from the spirit and scope of the invention.

This invention is claimed as follows:

1. An electric circuit breaker comprising a molded case, a pair ofseparable contacts in said case, a releasably latchable trip leverpivotally mounted in said case and releasable from a latched position toeffect separation of said contacts, an integral magnetic core andarmature support member disposed in said case and including a generallyU-shaped magnetic core portion and a generally U-shaped armature supportportion, and an armature pivotally mounted on said armature supportportion and having a free end portion normally spaced from and adaptedto be attracted toward said magnetic core portion to effect release ofsaid trip lever, the length of the leg portions of said magnetic coreportion measured from the bight portion thereof being at least as greatas the length of said bight portion measured between said leg portionsand the greater portion of the length of one leg portion of saidmagnetic core portion being free of direct connection to thecorresponding one leg portion of said armature support portion.

2. An electric circuit breaker as claimed in claim 1, wherein saidarmature support portion and said magnetic core portion are connectedsolely by a single fiat connecting portion.

3. An electric circuit breaker as claimed in claim 1, wherein saidarmature support portion and said magnetic core portion are connectedsolely by a connecting portion joining the other leg portion of saidmagnetic core portion with the corresponding other leg portion of saidarmature support portion.

4. An electric circuit breaker as claimed in claim 1, wherein the legportions of said magnetic core portion are longer than the leg portionsof said armature support portion.

5. An electric circuit breaker as claimed in claim 1, wherein the bightportions of said magnetic core portion and said armature support portionare oifset from each other.

6. An electric circuit breaker as claimed in claim 1, wherein saidintegral magnetic core and armature support member is pivotallyconnected to said case adjacent said armature support portion and saidmagnetic core portion is provided with a tongue anchored in said case,said tongue being bendable before installation of said integral magneticcore and armature support member in said case to predetermine the sizeof the air gap between said armature and said magnetic core portion.

7. An electric circuit breaker as claimed in claim 1, including a lineterminal electrically connected to a movable one of said contacts bothin an open and in a closed position thereof with respect to a stationaryone of said contacts by means including a formed electrically conductivestrap member disposed outside said magnetic core portion between saidmagnetic core portion and a wall of said case.

8. An electric circuit breaker as claimed in claim 1, including a lineterminal electrically connected to a movable one of said contacts bothin an open and in a closed position thereof with respect to a stationaryone of said contacts by means including an electrical conductor woundaround said one leg portion of said magnetic core portion.

9. An electric circuit breaker as claimed in claim 1, including abimetallic member in said case having a free end portion adapted to movesaid armature toward said magnetic core portion and a line terminalelectrically connected to said bimetallic member by means including anelectrical conductor formed of relatively high resistance wire and wounda plurality of times around said one leg portion of said magnetic coreportion.

References Cited by the Examiner UNITED STATES PATENTS 2,897,314 7/1959Cole 20088 2,902,560 9/1959 Stanback et al. 20088 3,098,136 7/1963Stanback et a1 20088 3,178,535 4/1965 Gelzheiser et al. 20088 BERNARD A.GILHEANY, Primary Examiner. R. N- ENVALL, JR., Assisiant Examiner.

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING A MOLDED CASE, A PAIR OFSEPARABLE CONTACTS IN SAID CASE, A RELEASABLY LATCHABLE TRIP LEVERPIVOTALLY MOUNTED IN SAID CASE AND RELEASABLE FROM A LATCHED POSITION TOEFFECT SEPARATION OF SAID CONTACTS, AN INTEGRAL MAGNETIC CORE ANDARMATURE SUPPORT MEMBER DISPOSED IN SAID CASE AND INCLUDING A GENERALLYU-SHAPED MAGNETIC CORE PORTION AND A GENERALLY U-SHAPED ARMATURE SUPPORTPORTION, AND AN ARMATURE PIVOTALLY MOUNTED ON SAID ARMATURE SUPPORTPORTION AND HAVING A FREE END PORTION NORMALLY SPACED FROM AND ADAPTEDTO BE ATTRACTED TOWARD SAID MAGNETIC CORE PORTION TO EFFECT RELEASE OFSAID TRIP LEVER, THE LENGTH OF THE LEG PORTIONS OF SAID MAGNETIC COREPORTION MEASURED FROM THE BIGHT PORTION THEREOF BEING AT LEAST AS GREATAS THE LENGTH OF SAID BIGHT PORTION MEASURED BETWEEN SAID LEG PORTIONSAND THE GREATER PORTION OF THE LENGTH OF ONE LEG PORTION OF SAIDMAGNETIC CORE PORTION BEING FREE OF DIRECT CONNECTION TO THECORRESPONDING ONE LEG PORTION OF SAID ARMATURE SUPPORT PORTION.